Search for charginos and neutralinos in e+e− collisions at = 189 GeV

Abstract

We report the result of a search for charginos and neutralinos, in e q e y collisions at 189 GeV centre-of-mass energy at LEP. No evidence for such particles is found in a data sample of 176 pb y1. Improved upper limits for these particles are set on the production cross sections. New exclusion contours in the parameter space of the Minimal Supersymmetric Standard Model are derived, as well as new lower limits on the masses of these supersymmetric particles. Under the assumptions of common gaugino and scalar masses at the GUT scale, we set an absolute lower limit on the mass of the lightest neutralino of 32.5 GeV, and a limit on the mass of the lightest chargino of 67.7 GeV for M-2 TeV.

Inert doublet model and LEP II limits

“…This method, which will be described in detail in Section III B, is careful enough to put more accurate limits on the H 0 and A 0 masses than the current existing estimates.. The different LEP experiments have separately searched for neutralinos via the production process e + e − →χ 0 1χ 0 2 followed by the decayχ 18,19,20,21]. The lightest neutralino,χ 0 1 , is assumed to be stable and would show up as missing energy, while the fermion pair, ff , could be detected as acollinear jets or leptons.…”

Direct probes ofR-parity-violating supersymmetric couplings via single-top-squark production

“…7 we show the mass contours for the t 1 , the χ 0 1 , and the χ ± 1 . A recent experimental lower bound of 80.5 GeV on the mass of the lightest chargino χ + 1 [23] is used to exclude regions (ex) of small m 1/2 . Regions in which tachyonic particles would be generated, electroweak symmetry would not be broken, or in which the lightest supersymmetric particle allows us to vary m t 1 without an appreciable change in the masses of the decay products and only a slow rise of sin θ t to 1.…”

Perturbative $$\lambda $$ λ -supersymmetry and small $$\kappa $$ κ -phenomenology

“…3 we show the parameter space in the twoparameter plane of m S and A λ , for λ = 1.2 and tan β = {4.5, 5, 5.5}, respectively. For each tan β region below the color contour is excluded by the condition of stability of the potential and the mass bound on the chargino mass m χ > 103 GeV [21][22][23]. The region in the right up corner is excluded by the precision measurement of Higgs coupling presently.…”